Lubricants containing synergistic wear inhibitors



United States Patent 3,360,463 LUBRICANTS CONTAINING SYNERGISTIC WEAR INHIBITORS James Keith Jacques, Walsall, England, assignor to Albright & Wilson (Mfg.) Limited, Oldbury, near Birmingham, England, a British company No Drawing. Filed Apr. 13, 1966, Ser. No. 542,222 Claims priority, application Great Britain, Apr. 15, 1965, 16,297/65 12 Claims. (Cl. 252-32.7)

ABSTRACT, OF THE DISCLOSURE Additive combinations suitable for addition to mineral oil lubricants containing a trialkylthiophosphite, wherein each alkyl group has from 6 to 18 carbon atoms, and a lead, zinc, molybdenum, nickel, chromium, or cuprous dialkyldithiophosphate, wherein each alkyl group has from 2 to 12 carbon atoms. The thiophosphite and trialkyldithiophosphite are in such proportions as to synergystically decrease wear on metal bearing surfaces lubricated by mineral oil lubricants containing one of said additive combinations.

The present invention provides improved lubricants. It is particularly concerned with mineral oil based lubricants modified to improve their anti-wear properties in respect of certain surfaces.

It is known that mineral oil lubricants may advantageously be modified by the addition of certain salts of dialkyldithiophosphoric acids. Such modified lubricants cause less corrosion of bearing surfaces than do unmodified mineral oils.

' We have now discovered that when thiophosphite esters and certain metal salts of dialkylthiophosphoric acids are jointly added in appropriate proportions to mineral oil lubricants, they exert a synergistic anti-Wear effect. We have discovered in particular that mineral oil lubricants suitably modified in this way, afford increased protection against polished wear when applied to steel bearings operating under high loads, and that certain of the modified lubricants show increased anti-wear properties when applied to aluminum and alloys thereof. Certain compositions also provide a synergistic improvement in anti-wear properties for low pressure lubrication of various metals.

Our invention accordingly provides a lubricant which ester and a dialkyldithiophosphate salt in such proportions as herein described that the thiophosphite and dialkyldithiophosphate act synergistically to improve the anti-wear properties of the mineral oil.

- A further aspect of our invention provides a composition suitable for addition to mineral oil lubricants which comprises a hydrocarbon thiophosphite and x percent (based on the total weightof the additive mixture) of a salt of the formula M v[(RO) PS where R is an alkyl group and M and x are suchthat: x lies between 10 and 98 where M is divalent zinc or divalent lead; at lies between 0.5 and '99 where M is molybdenum or monovalent copper; x lies between 55 and 98 where M is divalent nickel; x lies between 60 and 90 or 10 and 40 where M is divalent chromium; and n is the valency of the metal radical M.

The thiophosphite ester preferably has at least nine carbon atoms in hydrocarbon groups. Trialkyl esters are preferred to aryl esters, and particularly preferred are trialkyl esters of straight chain alkyl groups having from six to eighteen carbon atoms, for example trilauryl trithiophosphite.

The dialkyldithiophosphate preferably has at least four carbon atoms in alkyl groups, and most preferably six or comprises: a' mineral oil, a hydrocarbon thiophosphite Patented Dec. 26, 1967 more carbon atoms, for example a diisopropyldithiophsophate, a dioctyl dithiophosphate or a dilauryl dithiophosphate. It is preferred to add the thiophosphite-i-thiophosphate mixture in a proportion of less than 10% (for example from 0.2 to 5%) of the total weight of the final lubricant, and most preferably 0.5 to 2%.

The nature of the synergistic effect for a given metal surface is determined principally by the relative proportion of thiophosphite to thiophosphate. This latter relationship is critical, and the optimum synergistic effect occurs at different values of this parameter for thiophosphate salts of different metals. Certain metal thiophosphates give an anti-synergistic effect at some concentrations and a synergistic effect at others. The preferred proportions of thiophosphate to thiophosphite varying accordin g to the load applied to the bearing surface and the metal being lubricated. We have found that certain compositions show synergism at low pressure but not at higher pressure and vice versa.

The following summarises the results obtained at very high pressure (200 kg. on a four ball machine) and at a lower pressure (100 kg. on four ball machine), for lubrication of steel and aluminium. The Zinc salts gave a very useful improvement in anti-wear properties for steel at high pressure, which was markedly synergistic for additives containing between 30 and 70% by weight of the Zinc salt. The composition containing 50% zinc salt 50% thiophosphite was particularly effective in improving the anti-wear properties of the mineral oil base. At low pressures the zinc salt gave a less marked synergistic efifect for additives containing more than 30% and preferably from 50 to of the salt.

The zinc salt has been found especially valuable for the lubrication of aluminium at high pressure. Synergism is observed for mixtures in all proportions, and gives a particularly useful result for additives containing more than 50% by weight of zinc salt, perferably 70% to 90% by weight.

The lead salt was found especially valuable for lubricating steel bearings operating under a load 100 kg. The synergism was especially striking for compositions containing more than 12% by weight of lead salt. The preferred proportion of lead salt for this application was 14 to 50% by weight of the total additive, and especially 20 to 30% by Weight. For high pressure lubrication of steel, it is preferred to employ additives containing larger proportion of lead salt, e.g. more than 55% by weight and preferably to 90% by weight. Additives contain- 'ing the lead salt give particular improvements in respect of aluminium lubricate when the proportion of lead salt is greater than 28% by weight and preferably 35 to 80% by weight.

Nickel salts show a valuable overall improvement in anti-Wear properties for lubrication of steel at high pressure, giving a useful synergistic effect for proportions of nickel salt greater than 55 by weight of the total synergistic additive and preferably greater than 60%. Lubricants containing an additive with proportions by weight of nickel salt between 70% and of the total additive, with an optimum value of about 75%, showed better high pressure anti-wear properties for steel than any vother lubricant combination tested. At low pressure the nickel salt showed advantageous synergistic efiects over the same range of compositions, but the improvement was less marked. Proportions by weight of nickel salt less than 55 did not exhibit any useful synergistic increase in the anti-wear properties at low pressure.

Synergism was observed with high pressure lubrication of steel using cuprous and molybdenum salts with thiophosphite in all proportions. Both salts gave greatest synergism at high pressure for additives containingless than 50% by weight of the salt. At low pressure cuprous salts gave useful synergism in proportions less than 75% by Weight of salt, but molybdenum was anti-synergistic in all proportions.

Additives containing more than 55% and preferably 70 to 80% by weight of cuprous salts were useful in the lubrication of aluminium.

The chromium salt was only of value for steel at high pressure where it gave synergistic improvements in two in four ball machine fixed race tests as described in our British application No. 22,768/ 63 using four steel balls under a load of 200 kg. Table II gives similar results for tests performed under loads of 100 kg. In each experiment the chuck was rotated at 1400 rpm. for 2 minutes.

Table III relates to tests with three aluminium and one steel ball under a load of 100 kg. Table IV relates to experiments with three aluminium and one steel ball under a load of 200 kg.

TABLE I [Base oil= Complete welding: Base oil 1% trilauryl trithiophosphite=2.62 mm. scar] Zinc Nickel Cuprous Molyb- Chro- Lead Additive X Salt, Salt, Salt, denum mium Salt, mm. mm. mm. Salt, Salt, mm.

mm. mm.

99% Base Oil X thiophosphite- 2. 66 2. 51 2. 23. 2. 34 2. 25 .2. 19 99% Base Oil X thiophosphite. 2. 16 2. 48 2. 43 2. 42 2. 63 2. 32 99% Base Oil X 54% thiophosphite. 2. 56 2. 09 2. 47 2. 45 2. 36 2. 23 99% Base Oil 1 2. 50 2. 31 2. 73 2.82 2. 50 2. 19

TABLE II [Base il=3.55 mm. scar: Base oil 1% trilauryltrithiophosphlte=2.03 mm. scar] Zine Nickel Cuprous Molyb- Chro- Lead Additive X Salt, Salt, Salt, denum rmum Salt, mm. mm. mm. Salt, Salt, mm.

mm. mm.

99% Base Oil 1. 95 1. 70 0.82 1. 84 2. 06 0. 73 99% Base Oil 0.56 1. 75 0.80 1.82 2. 02 0. 81 99% Base Oil 0.75 0.61 0. 16 1. 76 1. 85 0. 84 99% Base 011 0.75 0. 72 0.82 0. 48 0.68 0. 88

TABLE III [Aluminium/steel,/100 kg. (1% 'IL'ITP alone in base oil gave a 0.98 mm. scar)] Zinc Nickel Cuprous Molyb- Chro- Lead Additive X Salt, Salt, denum mium Salt, mm. mm. mm. Salt, Salt, mm.

mm. mm.

99% mineral oil, 1% X, 0% 'ILTTP 0. 94 0.96 0.92 0.91 1.02 0.97 99% Mineral oil, X, TLTTP. 1.08 0.97 0. 85 0. 95 1.10 0.89 99% mineral oil, X, 'ILTTP- 0. 94 0. 96 0. 95 0. 92 1. 0.91 99% mineral oil, X, TLTTP 0. 94 1.01 0. 94 0.96 1.07 1. 01

TABLE IV [Aluminium/steel, 200 kg. (Base oil alone gave 1.69 mm scar)] Lubricant:

Percent mineral oil 95 95 95 95 95 95 95 95 Percent Zn diiso ropyl dithiophosphate. 0 1. 2. 50 3. 12 3. 75 4. 37 4. 68 5 Percent trilaury trithiophosphite 5 3. 75 2. 50 1. 88 1. 25 0. 63 0. 32 0 Seat diameter (mm.) 1. 62 1. 45 1. 44 1. 1. 31 1. 30 1. 36 1. 39

ranges of proportions; the most marked being for compositions containing less than of the chromium salt, and the other being for compositions containing more than 65% salt.

Both the chromium and the molybdenum salts were anti-synergistic when used for the lubrication of aluminium surfaces.

Those zlubricants of our invention which are recommended for lubrication of steel bearings under high pressure conditions have been found particularly useful in inhibiting polished wear. This is a problem which is increasingly important as a reason for the failure of cams and tappets in engines of high compression ratio, and existing sump oils are inadequate to prevent it.

The following tables list results which were obtained in anti-wear experiments using as lubricant various mixtures of ,trilauryltrithiophosphite with diiso'propyldithiophosphate salts in mineral oil and which illustrateour invention. Table I relates to the mean scar diameter obtained Lubricant compositions according to our invention may additionally contain such additives e.g. antioxidants as are conventionally used in the preparation of lubricants.

I claim:

1. A lubricant additive combination consisting essentially of a trialkylthiophosphite ester wherein each alkyl group has from 6 to 18 carbon atoms, and x percent based on the total weight of said additive combination, of a dialkyldithiophosphate salt of the formula M[(RO) lE'S wherein R is an alkyl group having from 2 to 12 carbon atoms, M is selected from divalentlead, zinc, molybdenum, nickel, chromium, and monovalent copper, n is the valency of the metal radical M, and x is a number such that where M is zinc or lead at has a value between 10 and 98; where M is molybdenum or copper x has a value between 0.5 and 99; where M is nickel x has a value between 55 and 98; and where M is chromium x has a value between 60 and 90.

2. A lubricant composition consisting essentially of a mineral oil, and the lubricant additive combination of claim 1.

3. The lubricant composition of claim 2 containing between 0.2 and 10% by weight of said additive combination.

4. The lubricant composition of claim 3 wherein said additive combination contains at least 30% by Weight of a zinc dialkyldithiophosphate.

5. The lubricant composition of claim 4 wherein said zinc salt is present in a proportion of up to 70% by weight of said additive combination.

6. The lubricant composition of claim 2 wherein said additive combination contains from 14 to 50% by Weight of a lead dialkyldithiophosphate.

7. The lubricant composition of claim 6 wherein the additive combination contains from 20 to 30% by weight of the lead dialkyldithiophosphate.

8. The lubricant composition of claim 2 wherein said additive combination contains from 80 to 90% by weight of a lead dialkyldithiophosphate.

9. The lubricant composition of claim 2 wherein said additive combination contains from 70 to 85% by weight of a nickel dialkyldithiophosphate.

10. The lubricant composition of claim 2 containing from about 0.2 to by weight of said additive combination.

11. The lubricant composition of claim 2 containing from about 0.5 to 2% by weight of said additive combination.

12. A lubricant composition consisting essentially of a mineral oil, and a trialkylthiophosphite ester wherein each alkyl group has from 6 to 18 carbon atoms, and a dialkyldithiophosphate metal salt of the formula wherein R is an alkyl group having from 2 to 12 carbon atoms, M is selected from divalent lead, zinc, molybdenum, nickel, chromium, and monovalent copper, and n is the valency of the metal radical M; in such proportions that the trialkylthiophosphite ester and said metal salt act synergistically to reduce the wear on metal bearing surfaces.

References Cited UNITED STATES PATENTS DANIEL E. WYMAN, Primary Examiner.

PATRICK P. GARVIN, Assistant Examiner. 

1. A LUBRICANT ADDITIVE COMBINATION CONSISTING ESSENTIALLY OF A TRIALKYLTHIOPHOSPHITE ESTER WHERIN EACH ALKYL GROUP HAS FROM 6 TO 18 CARBON ATOMS, AND X PERCENT BASED ON THE TOTAL WEIGHT OF SAID ADDITIVE COMBINATION, OF A DIALKYLDITHIOPHOSPHATE SALT OF THE FORMULA M((RO)2PS2)N WHEREIN R IS AN ALKYL GROUP HAVING FROM 2 TO 12 CARBON ATOMS, M IS SELECTED FROM DIVALENT LEAD, ZINC, MOLYBDENUM, NICKEL, CHROMIUM, AND MONOVALENT COPPER, N IS THE VALENCY OF TEH METAL RADICAL M AND X IS A NUMBER SUCH THAT WHERE M IS ZINC OR LEAD X HAS A VALUE BETWEEN 10 AND 98; WHERE M IS MOLYBDENUM OR COPPER X HAS A VALUE BETWEEN 0.5 AND 99; WHERE M IS NICKEL X HAS A VALUE BETWEEN 55 AND 98; AND WHERE M IS CHORMIUM X HAS A VALUE BETWEEN 60 AND
 90. 